/usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so is in libgl1-mesa-dri 10.3.2-1+deb8u1.
This file is owned by root:root, with mode 0o644.
It is a symlink to /usr/lib/x86_64-linux-gnu/dri/./usr/lib/x86_64-linux-gnu/dri/nouveau_dri.so